The present invention concerns grids for positive electrodes in electrical lead storage batteries and particularly grids made from lead alloys which are free of antimony or contain only a small amount of antimony. The invention can be applied to all types of positive lead electrodes.
Grids for lead electrodes of electrical storage batteries, both positive and negative electrodes, have been made for many years of cast lead alloys, generally containing 6 to 12 percent antimony. While the antimony has been added primarily to improve the mechanical properties of the grid, it has also affected the physical structure and the electrochemical conditions in the battery cells. The antimony added to the grid alloy has contributed many advantages but it has also resulted in the important disadvantage of the so-called antimony poisoning of the negative electrode.
In order to counteract antimony poisoning, electrode grids have been produced of an antimony-free lead alloy and such grids have been used in lead storage batteries either solely for the negative electrodes or for both the positive and negative electrode. Since antimony migrates through the electrolyte from the positive electrode to the negative electrode, it has been proven insufficient to construct the grid for only the negative electrode from antimony-free lead alloys. There has therefore been an effort to make all electrode grids from antimony-free alloys and batteries incorporating such grids are produced to a limited extent. The absence of antimony from grid alloys, however, has led to other problems. There have been attempts to counter these problems in various ways, for example, by mixing antimony compounds in the active mass of the electrodes, or by making the electrode grid from alloys containing a small quantity of antimony. It has been found, though, that in order to avoid the disadvantages which are connected with antimony-free alloys, the amount of antimony in the alloys had to approach 3 to 5 percent by weight. At this level of antimony content, however, antimony poisoning of the negative electrode still occurs, even though its effect may appear after a longer time and be less powerful than at the more conventional higher levels of antimony content.
The use of antimony-free alloys at the boundary layer between grid and active material can give rise to conditions which can, among other things, cause high charging potential at the electrode grid, at least in the beginning of the charging process. The application of a thin outer layer of pure antimony to antimony-free grids has therefore been tried. Investigations have shown, however, that such grids show approximately the same high charging potential as antimony-free grids under the same conditions. It has been determined, therefore, that none of the above-mentioned methods for avoiding the effects which appear, for example, as high charging potentials have led to the desired results.
It has also been proposed, see U.S. Pat. No. 2,282,760, to form the grid of a base or support made of a conventional lead alloy obtaining a relatively high antimony content (e.g., 12 or 13 weight percent antimony, balance lead) and to coat the support with a lead alloy containing less than 0.5 (generally less than about 0.2) weight percent antimony. The absence of antimony from the grid surfaces in contact with the active material has led to other problems, however, and the use of such construction has not proven commercially attractive.